Integrate gitlab-ci/show-instructions-if-merge-fails and 2 more

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Commit: https://gitlab.com/garz-fricke/yocto/infrastructure/gitlab-ci/-/commit/a497a5705c4cbfa2a03f5241fc79bc3c9f7869da

deploy_gitlab_ci: show instructions if merge fails

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Commit: https://gitlab.com/garz-fricke/yocto/infrastructure/gitlab-ci/-/commit/01d10faba45c1cd1a69bff062d43aa1fa82562bd

update_submodule: fix accidental multi-commits

If integration branch already existed and had to be replaced, the new commit was accidentally pushed on top of the already existing commit instead of replacing it. Fixed this by checking out the master branch again before creating the commit.

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Commit: https://gitlab.com/garz-fricke/yocto/infrastructure/gitlab-ci/-/commit/d887beddab2db961e3d6e04cdf90c1b305bc0764

list_commits: replace "---" with "--"

GitLab renders "---" as a horizontal line or as a frame. We do not want this, so replace it with "--".